Commutator having commutating segments adhesively bonded in shear to a base member

ABSTRACT

A commutator in which a base member having a mounting portion of substantial axial extent and an annular planar surface axially facing the mounting portion has electrically conductive commutating segments secured to the mounting portion. Each commutating segment has a planar surface at an end thereof closely adjacent the annular planar surface, and the end planar surface is adhesively bonded to the annular planar surface by a relatively thin layer of adhesive material which is electrically conductive and has high dielectric strength. The thickness of the adhesive layer is sufficiently small that the bonds between the layer and the adjacent surfaces are substantially stressed in shear during operation of the commutator in a dynamoelectric machine.

United States Patent 1 1 Cole [ 1 Aug. 7, 1973 [75] Inventor:

[73] Assignee: General Electric Company, Lynn,

Mass.

22 Filed: Mar.1, 1972 211 App]. No.: 230,677

Quintin Perry Cole, Erie, Pa.

2,990,488 6/1961 Schafer 310/235 2,956,190 10/1960 Bechstein 310/235FOREIGN PATENTS OR APPLICATIONS 7/1968 Great Britain 310/233 PrimaryExaminer-R. Sku'cly Att0rneyJames C. Davis, Jr. et a1.

[57] ABSTRACT A commutator in which a base member having a mountingportion of substantial axial extent and an annular planar surfaceaxially facing the mounting portion has electrically conductivecommutating segments secured to the mounting portion. Each commutatingsegment has a planar surface at an end thereof closely adjacent theannular planar surface, and the end planar surface is adhesively bondedto the annular planar surface by a relatively thin layer of adhesivematerial which is electrically conductive and has high dielectricstrength. The thickness of the adhesive layer is sufficiently small thatthe bonds between the layer and the adjacent surfaces are substantiallystressed in shear during operation of the commutator in adynamoelectric'machine.

8 Claims, 5 Drawing Figures abandoned.

52 us. C1. 310/235, 310/236 [51] Int. Cl. H02k 13/04 [58] Field ofSearch 310/233, 234, 235, 310/236; 29/597; 252/514; 264/272 [56]References Cited UNITED STATES PATENTS 3,473,063 10/1969 Forste 310/2352,645,732 7/1953 Marsal 310/236 2,645,733 7/1953 Marsal 310/2353,290,527 12/1966 Hahcrmann 310/236 1,401,708 12/1921 Kcmpton 1. 310/23628 e g os PATENIED 3.751.700

'SHEEI 2 BF 3 PAHNIED M 3.751.700

sum 3 or 3 FIG. 4

COMMUTATOR HAVING COMMUTATING SEGMIEN'IS ADHESIVELY BONDED IN SHEAR TO ABASE MEMBER RELATED APPLICATIONS This application is acontinuation-inpart of copending patent application Ser. No. 77,071, nowabandoned for Bonded Commutator Having Improved Peel Resistance, filedon Oct. 1, 1970 in the name of Quintin P. Cole and assigned to theassignee of this application. The invention of this application is alsorelated to the invention described and claimed in copending patentapplication Ser. No. 77,130, now abandoned (Docket No. 2l-DC-l69) forAdhesively Bonded Commutator, filed on Oct. 1, 1970 in the name of JohnF. Binder and also assigned to the present assignee, this inventioncomprising an improvement on the commutator construction of applicationSer. No. 77,130, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to adhesively bonded commutators for use in dynamoelectricmachines and, more particularly, to such commutators in which theretention of commutating segments is enhanced by adhesive bonds stressedin shear during commutator operation.

2. Description of the Prior Art D-C motors and generators of theindustrial type include as an important component thereof a cylindricalrotating commutator having a plurality of spaced-apart commutatingsegments on the outer periphery thereof. Since in an industrial typemachine each commutating segment must be capable of conductingsubstantial amounts of electrical current, the commutating segments havesubstantial mass and, as a result, are subject to substantialcentrifugal forces during normal operation. These centrifugal forcesmust obviously be resisted in order to maintain the integrity of thestructure. It is not, however, sufficient that the commutator merely beheld together mechanically during operation; it is also essential thatthe structure exhibit a high degree of mechanical and thermal stabilitythroughout the entire operating range. It has been found that mechanicaland thermal instability resulting from uneven heating, rapidacceleration and deceleration, and the like can result in heavy,intolerable sparking and excessive wear and damage to not only thecommutator, but also other machine components such as the brushes incontact with the commutator.

By the invention of patent application Ser. No. 230,676, adhesivelybonded commutators having a high degree of mechanical and thermalstability have been developed. Under most conditions, these adhesivelybonded commutators retain their integrity well. It is possible, however,by mechanical shock to the exposed segment ends at the front end of thecommutator, i.e., at the end of the commutator away from the armaturecore, to overstress the adhesive bond between the metallic commutatorsegments and the outer cylindrical surface of the base member.Thereafter,

failure of the commutator assembly may occur through gradual lifting orpeeling of the commutation segment from the front end of the commutatorsegment to the end thereof near the armature core.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide an improved commutator of the adhesively bonded type.

Another object of this invention is to provide an adhesively bondedcommutator in which commutating segments are secured to a base memberwith a high de gree of peel resistance.

Yet another object of this invention is to provide an adhesively bondedcommutator in which the ends of commutating segments are substantiallyprotected against certain mechanical shocks and resulting separa tionfrom a base member through progressive peeling action.

Briefly stated, in carrying out the invention in one form, a commutatorincludes a base member having a mounting portion of substantial axialextent and an annular planar surface at an end of the mounting portionaxially facing the mounting portion. A plurality of electricallyconductive commutating segments are peripherally secured to the mountingportion, each of the commutating segments having a planar end surfaceparallel to and closely adjacent the annular planar surface. A layer ofadhesive material is interposed between the end planar surfaces to theannular surface, the adhesive material preferably being selected fromthe group of adhesives consisting of epoxies and polyimides. Inaccordance with the invention, the thickness of the adhesive layer issufficiently small, preferably less than 0.020 inch, to assure that thebonds of the adhesive layer with the end surface of the commutatingsegments and the annular planar surface will be sub- .stantiallystressed in shear before any separation will occur between thecommutating segments and the mounting portion. Furthermore, the portionof the base member defining the annular planar surface substantiallyprotects the adjacent ends of the commutating segments against certainforms of mechanical shock, thereby also helping prevent initialseparation of the segments from the axial mounting portion. By a furtheraspect of the invention, spacing means are provided for maintaining apredetermined minimum thickness of the adhesive layer.

BRIEF DESCRIPTION OF THE DRAWINGS This invention may be betterunderstood by reference to the following detailed description taken inconjunction with the accompanying drawings in which:

FIG. I is a perspective view of an armature for a typicalindustrial'type dynamoelectric machine incorporating a commutator of thepresent invention;

FIG. 2 is a longitudinal cross sectional view of the commutator shown inFIG. 1;

FIG. 3 is a cross sectional view of the commutator taken along viewingline 33 of FIG. 2,

FIG. 4 is a perspective view of the commutator segment used in thecommutator of this invention; and

FIG. 5 is an enlarged view of a portion of the adhesive layers betweenthe base member and one of the commutating segments.

DETAILED DESCRIPTION Referring first to FIG. I, there is shown anarmature assembly 10 for an industrial-type dynamoelectric machine,including specifically armature coils l2, armature shaft 14 and acommutator assembly which includes a base member 16 and elongatedcommutation segments 18 mounted thereon. The axially inner ends ofsegments 18a are in electrical contact with armature coils 12 throughlead wires 12a.

The commutator of FIG. I is shown in longitudinal and radial crosssection in FIGS. 2 and 3, respectively. As shown therein, the basemember 16 includes a primary mounting portion 22 having a cylindricalouter surface 24 peripherally surrounding a central axis 26 and anoutwardly projecting annular flange 28 at the axially outer end of thebase member 16. The flange 28 forms an annular planar surface 30 axiallyfacing the mounting portion 22 and its cylindrical surface 24. Thecommutating segments 18 are peripherally spaced about the cylindricalsurface 24 and are adhesively bonded thereto by a layer 34 of adhesivematerial. In addition,each commutating segment 18 has an end planarsurface 36 at its outer end, the segments 18 also being adhesivelysecured to the base member 16 by a layer 38 of adhesive material betweenthe end surfaces 36 and the annular planar surface 30. As bestillustrated by FIG. 4, each of the segments 18 is of relatively simpleshape with a rectangular cross section. This is in contrast to thecomplex shapes of the typical prior art commutating segments forindustrial type dynamoelectric machines. The commutator of thisinvention may be easily mass produced in that the commutating segments18 may be simultaneously positioned and secured to the base member 16. Apreferred assembly method, and preferred apparatus for carrying out themethod, are disclosed and claimed by copending patent application Ser.No. 7 7,131, now abandoned for Method and Apparatus For AdhesivelyBonded Commutators," filed on Oct. 1, 1970, in the name of Mi-' chael A.McGrath and assigned to the assignee of this invention.

In accordance with the invention'of copending patent application Ser.No. 230,676, the base member 16 is made from a material characterized byextreme rigidity and thermal stability relative to that of the adhesivematerial forming the bonding layers 34 and 38. It has been found inpractice that steel is a particularly suitable material for the basemember 16 in that it is extremely rigid relative to common adhesives andhas a low coefficient of expansion, on the order of 3.5 X in./in./ C,relative to suitable adhesives, which generally have coefficients ofexpansion in the range of 30 X 10 in./in./ C to 60 X l0 in./in./ C.Under suitable conditions, the base member 16 may be made of variousmetallic and non-metallic materials, or combinations thereof, dependingon cost and mechanical stress and environmental conditions in theultimate intended application. Those prepared from electrically conduc-'tive materials must of course be insulated from the commutator segment.In the case of metallic base members, steel, aluminum, cast iron, etc.may be used with an insulating covering or coating consisting of moldedepoxy glass, molded polyimide glass, or plasma sprayed ceramic. Apreferred embodiment is a steel base member having a plasma sprayedalumina outer coating 40 as illustrated by FIG. 2. v

The commutator segments 18 used in the present invention may be madefrom rectangular or bevelled metal stock. Generally, they are made ofcopper or a copper alloy selected for specific properties, althoughaluminum and other metals may be used. When rectangular cross sectionstock is used, rounded or radiused edges are provided on the bondingsurface thereof to minimize stress concentration at the outer limits ofthis bonding surface. If the segment is made of copper, generally it isdegreased with solvent and then acid (bright) dipped prior to bondingthe segment to the base member In some cases, it may be desirable tohave a thin layer of zinc diffused on the surface of the copper segment.Among other things, this may improve the bondability of the coppersegments. Such a layer may be provided by degreasing with solvent, acidbright dipping, cyanide cleaning, plating the copper segments and thenzinc anthen diffusing the zinc into the copper by heat treating it at180250 C.

Depending on the assembly method used, the commutator segments may thenbe coated on their bonding surfaces with the adhesive to be used ordelivered directly to the assembly apparatus. Alternatively, theadhesive may be applied to the copper segment in the assembly apparatusor it may be applied to the base member to which the segments are to bebonded. This may depend, among other things, on the design of theassembly apparatus and the assembly procedure used. Generally, if thebase member is heated prior to the assembly, the adhesive is applied tothe segment rather than to the base member to avoid prematureactivation. If ultrasonic vibration is used to provide activationenergy, the adhesive may be applied to either the segment or the basemember. Application of the adhesive to the segment is preferred in mostcases.

The adhesive is generally applied as a viscous liquid and a roller,liquid dispenser, or spray form of application may be used. Such viscousliquid adhesive also includes a spacing filler, such as glass beads 42(see FIG. 5), to keep the adhesive from being squeezed out from betweenthe segment and the mounting surfaces 24 and 30, thereby starving thebond interfaces of adhesive material. Alternatively, adhesives disposedin a sheettype supply means can be applied by wrapping the sheet aroundthe commutator shell and placing a sheet adjacent the annular surface30. Hot melt adhesives may be applied by spray, electrostatic, or fluidbed techniques and combinations of these techniques can also be usedwith hot melt adhesives. For more detailed consideration of appropriatebonding methods, attention is directed to the said copending applicationSer. No. 77,13l, now abandoned.

The details of the various adhesive compositions which may be used willbe described below.

As taught by the aforesaid patent application Ser. No. 230,676, theadhesive used to provide the bonding layer 34 must be capableofproviding a high strength bond when stressed in tension. Further, theadhesive must be electrically non-conductive and have good dielectricstrength. The former characteristic is necessary to avoid arc-overbetween commutation segments at the base thereof due to adhesivematerial around the commutation segments while the latter characteristicis necessary to avoid voltage-induced breakdown of the adhesive materialdue to voltage differentials between commutation segments and therotating base element to which the segments are mounted. Further, it isdesirable that the adhesive be capable of withstanding high temperaturessince such temperatures are often encountered in larger d-c motors andgenerators. Of course, the adhesive must also have good agingcharacteristics. As pointed out in the aforesaid patent application Ser.No. 230,676 certain heat cured epoxies and polyimides have been found tobe particularly effective in providing the bonding layer 34. Fordisclosure of specific resins suitable for use as the adhesive material,attention is directed to the said copending patent application.

As pointed out previously, the annular flange 28 protects the axiallyouter ends of the commutating segments 18 against mechanical abuse anddamage. Through this protection, the integrity of the adhesive layer 34and its bonds with the segments 18 and the cylindrical surface 24 at theouter ends of the segment 18 is greatly enhanced. As a result,progressive peeling of the segments 18 from an initial bond failure atthe outer ends thereof is substantially prevented. To furtherprotectagainst such progressive failure, the layer 38 of adhesivematerial is provided in accordance with this invention between theannular planar surface 30 and the end surfaces .36 of the segments l8.Since, however, adhesive materials such as epoxies and polyimides haverelatively low sheat modulii, it is not sufficient that there merely beprovided a layer 38 of adhesive material. If the layer 38 wererelatively large, say 0.250 inch, the layer 34, which in accordance withthe aforesaid application Ser. No. 230,676 should not exceed 0.020 inchin thickness, would fail and be progressively peeling long before theradial movement of the outer end of the segment 13 would be sufficientto place any significant shear load on the bonds of the layer 38. Toprotect against progressive peeling, it is essential that the layer 38relieve the layer 34 bycarrying in shear a significant portion of thetotal force holding the segment 18 on the base member 16. To accomplishthis, it has been found in accordance with the present invention thatthe layer 38 should also be relatively thin so that it is substantiallystressed in shear during operation of the commutator in a dynamoelectricmachine.

As taught in the aforesaid patent application Ser. No. 230,676, thethickness tof the adhesive layer 34 must be maintained with apredetermined range relative to the diameter D of the base member 16.More particularly, it has been found in practice that the assembledcommutator will substantially exhibit the mechanical and thermalstability characteristics of the base member 16 if the diameter D ismaintained at least one hundred times as great as the thickness t.'lfthe thickness t is permitted to become relatively greater, the greaterflexibility and the higher coefficient of expansion of the adhesivematerial will cause the characteristics of the integral commutator todepart noticeably and considerably from the characteristics of the basemember.

Still more particularly, the commutating segments 18 should not beforced onto the cylindrical surface 17 of the base member to withsufficient force to squeeze the adhesive material from between themember. In other words, it has been found that a minimum thicknessshould be maintained. To assure that this minimum spacing is maintained,it is convenient to provide small glass heads 32 or other spacing meansin the adhesive material to prevent the formation of a dry joint. Inmost applications, it is desirable that the beads 42 have a diameter ofapproximately 0.003 inch. in other cases, however, it may be desirableto permit the thickness 1 to be as small as 0.001 inch, or it may bedesirable to maintain a larger minimum spacing. On the other hand, ithas been found that the thickness of the layer of adhesive materialshould not exceed approximately 0.020 inch. Since the base member 16will normally have a diameter D of at least 2.000 inches, it will beseen that the desired relationship between t and D will be maintainedeven at the minimum diameter D and the maximum thickness t. Inaccordance with this invention, it has been found that the layer 38 willbe substantially stressed in shear during operation if it too ismaintained at a thickness 1 of 0.020 inch or less. A minimum thicknessshould also be maintained, the glass beads 42 or other spacers beinguseful for preventing the formation of a dry joint. While not absolutelyessential, it is preferable that the two layers 34 and 38 haveessentially the same thickness. in any event, the thickness of the layer38 should be sufficiently small relative to the thickness of the layer34 to assure that the bonds of the layer 38 will be substantiallystressed in shear during operation.

In view of the foregoing, it will be seen that this invention providesan improved commutator for dynamoelectric machines in which thecommutating segments are secured to a base member with a high degree ofpeel resistance.

The foregoing is a description of illustrative embodiments of theinvention, and it is applicant's intention in the appended claims tocover all forms which fall within the scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. For use in a dynamoelectric machine, a commutator comprising:

a base member having a mounting portion of substantial axial extentperipherally surrounding a central axis and an annular planar surfacenormal to said central axis at an end of said mounting portion, saidannular planar surface axially facing said mounting portion,

a plurality of elongated, electrically conductive commutating segmentsperipherally spaced about said mounting portion and secured thereto,each of said commutating segmentshaving a planar surface at an endthereof parallel to and closely adjacent said annular planar surface,

and a layer of high temperature resistant adhesive material interposedbetween the end planar surface of each of said commutating segments andsaid annular planar surface to bond said commutating segments to saidannular planar surface, said adhesive material being electricallynon-conductive and having high dielectric strength,

the thickness of said layer of adhesive material being sufficientlysmall that the bonds of said layer with said annular planar surface andsaid end planar surface are substantially stressed in shear duringoperation of the commutator in a dynamoelectric machine.

2. A commutator as defined by claim I in which the thickness of saidlayer of adhesive material is in the range of 0.020 inch or less.

3. A commutator as defined by claim I in which said adhesive material isselected from the group of adhesives consisting of epoxies andpolyimides.

4. A commutator as defined by claim 3 in which said mounting portion ofsaid base member comprises a cylindrical outer surface, a layer of saidadhesive material being interposed between each of said commutatingsegments and said cylindrical surface to adhesively bond saidcommutating segments to said cylindrical surface.

5. A commutator as defined by claim 4 in which said base member isformed of a material characterized by extreme rigidity and thermalStability relative to said adhesive material, the diameter of saidcylindrical surface being at least one hundred times greater than the Ithickness of said layer of adhesive material so that the commutatorsubstantially exhibits during operation in a dynamoelectric machine themechanical and thermal stability characteristics of said base member.

6 A commutator as defined by claim in which the diameter of said basemember is at least 2.000 inches and thethickness of each of saidadhesive layers belindrical surface.

2. A commutator as defined by claim 1 in which the thickness of saidlayer of adhesive material is in the range of 0.020 inch or less.
 3. Acommutator as defined by claim 1 in which said adhesive material isselected from the group of adhesives consisting of epoxies andpolyimides.
 4. A commutator as defined by claim 3 in which said mountingportion of said base member comprises a cylindrical outer surface, alayer of said adhesive material being interposed between each of saidcommutating segments and said cylindrical surface to adhesively bondsaid commutating segments to said cylindrical surface.
 5. A commutatoras defined by claim 4 in which said base member is formed of a materialcharacterized by extreme rigidity and thermal stability relative to saidadhesive material, the diameter of said cylindrical surface being atleast one hundred times greater than the thickness of said layer ofadhesive material so that the commutator substantially exhibits duringoperation in a dynamoelectric machine the mechanical and thermalstability characteristics of said base member.
 6. A commutator asdefined by claim 5 in which the diameter of said base member is at least2.000 inches and the thickness of each of said adhesive layers betweensaid commutating segments and, respectively, said cylindrical surfaceand said annular planar surface is in the range of 0.020 inch or less.7. A commutator as defined by claim 6 further comprising spacing meansdisposed in said layer of adhesive material for establishing a minimumthickness of said adhesive layer.
 8. A commutator as defined by claim 6in which said base member is comprised of steel having a coating ofalumina on both said annular planar surface and said cylindricalsurface.